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Fipronil is a phenylpyrazole insecticide that is widely used in residential and agricultural settings to control ants, roaches, termites, and other pests. Fipronil and its transformation products have been found in a variety of environmental matrices, but the source[s] which makes the greatest contribution to fipronil in surface water has yet to be determined. A sampling effort designed to prioritize known fipronil inputs (golf courses, residential areas, biosolids application sites and wastewater facilities) was conducted in North Carolina to learn more about the origins of fipronil in surface water. High resolution mass spectrometry (HRMS) analysis indicated that fipronil and its known derivatives were routinely present in all samples, but concentrations were substantially elevated near wastewater treatment plant outfalls (range 10-500 ng/L combined), suggesting that they predominate as environmental sources. Corresponding recycled wastewater samples, which were treated with NaOCl for disinfection, showed disappearance of fipronil and all known degradates. HRMS and nuclear magnetic resonance (NMR) analysis techniques were used to determine that all fipronil-related compounds are oxidized to a previously unidentified fipronil sulfone chloramine species in recycled wastewater. The implications of the presence of a new fipronil-related compound in recycled wastewater need to be considered. Published by Elsevier B.V.